This invention relates to presses. In particular, this invention relates to an actuator particularly suitable for use with an injection or extrusion molding press, and a method of clamping a press.
Presses have many uses, one of the most popular being to clamp mold parts together in an injection molding apparatus. In a conventional injection molding apparatus a press section is disposed behind a plastic injection section. The press includes a moving platen which is forced toward a stationary platen by at least one actuator, usually a hydraulic cylinder mounted at the rear of the apparatus. The actuator bears against a stationary rear frame or xe2x80x9cspiderxe2x80x9d, which supports upper and lower pairs of guide bars that maintain the moving and stationary platens (and thus the mold parts) in precise alignment as the actuator forces the moving platen toward the stationary platen and into the clamping position.
Typically a hydraulic press is used in an injection molding apparatus, due to the very high forces required to properly clamp the mold parts together. In a conventional hydraulic actuator the hydraulic cylinder must be longer than the length of a full stroke of the piston and must be oriented in the direction of the stroke. Since the injection molding apparatus occupies the space in front of the press, the hydraulic cylinder is conventionally mounted to the rear of the press and thus a large clearance is required behind the operative clamping portion of the press in order to accommodate the cylinder.
Moreover, in a conventional hydraulic press the hydraulic cylinder serves the sole purpose of actuating the moving platen, and separate guide bars are used to maintain the moving and stationary platens in precise alignment. The use of separate structures for these purposes results in an expensive and heavy apparatus which makes poor use of available space. Also, the use of a heavy hydraulic cylinder capable of applying the necessary clamping force to both clamp and move the platen increases the weight and cost, and reduces the speed, of the apparatus.
It would accordingly be advantageous to provide a hydraulic press in which the actuating cylinders can be reduced in length and contained within the operative clamping section of the press, to significantly reduce the space requirements of the overall apparatus and thus allow plastics fabricators to utilize production facilities more efficiently.
It would also be advantageous to provide a press which combines the actuating and platen alignment functions of the press into the same structure, to reduce the weight and cost of the apparatus, and to provide an actuator which provides both actuating and clamping functions but without sacrificing speed or unduly increasing the cost and weight of the apparatus.
It would also be advantageous to provide a press that operates in two directions, taking advantage of the reciprocating motion of the actuator, to provide two injection molding cycles within a single press cycle.
The present invention overcomes these disadvantages and provides an economical, lightweight and compact press, and injection molding apparatus utilizing the press, incorporating an actuator which provides both actuating and clamping functions. The actuator of the invention may be used in virtually any application in which a clamping force is required, the actuator of the invention being particularly advantageously used with an injection molding press in an injection molding apparatus.
In one preferred embodiment the actuator is incorporated into a tandem press having a moving frame comprising a moving platen moving in a reciprocating motion between stationary outer platens. The moving platen moves on a track between a first clamping position in which the moving platen clamps a first mold mounted on one side of the press, and a second clamping position in which the moving platen clamps a second mold on the other side of the press. Because of the tandem design, as one mold is moved to a clamping position the other mold is being separated to remove a molded article. The tandem press of the invention thus provides two complete clamping cycles within one press cycle.
In the preferred embodiment an actuator according to the invention also serves as guide bars for maintaining the moving platen in alignment with the stationary platens. The tandem press of the invention thus avoids the need for separate guide bars by providing hydraulic actuating cylinders mounted on the stationary platens, the pistons for which serve both as guide bars to maintain alignment between the platens and as actuators to move the moving platen between clamping positions. In the preferred embodiment the actuating cylinders provide a relatively low force and operate at high speed, and the moving platen is provided with hydraulic clamping cylinders operating more slowly but with a relatively high force to apply the required clamping force to the mold after the actuating cylinders have moved the moving platen to the clamping position.
The present invention thus provides an actuator for actuating opposed first and second structures, the first and second structures being movable between an open position in which the first and second structures are spaced apart, and a closed position in which the first and second structures are disposed together, comprising: at least one hydraulic actuating cylinder mounted to the first structure, having an inner end facing the second structure and an outer end, at least one hydraulic clamping cylinder mounted to the second structure, a piston extending out of both ends of the actuating cylinder, having a first portion providing a piston head disposed within the actuating cylinder and a second portion providing a piston head disposed within the clamping cylinder, and a piston lock for anchoring the piston, whereby the actuating cylinder can be actuated to move the first and second structures from the open position to the closed position, and when the piston is anchored in the closed position the clamping cylinder can be actuated to apply a clamping force between the first and second structures.
In further aspects of the actuator of the invention: the clamping cylinder has a larger diameter than the actuating cylinder; the piston lock comprises an enlargement at portion of the piston projecting beyond the outer end of the actuating cylinder; the piston lock further comprises a spacer which in an anchoring position cooperates with the enlargement to substantially prevent the piston from extending toward the second structure; the first structure is stationary and the second structure is movable; the first structure comprises a stationary frame comprising at least one stationary platen having a working face, and the second structure comprises a moving frame comprising a moving platen disposed in alignment with the stationary platen and having a working face in opposition to the working face of the stationary platen, the movable platen being movable toward and away from the stationary platen and in a clamping position applying a clamping force between the working face of the stationary platen and the working face of the moving platen; the stationary frame comprises a first stationary platen having a working face and a second stationary platen having a working face disposed in opposition to the first stationary platen, each stationary platen and the moving frame comprises a moving platen disposed between the first and second stationary platens and in alignment therewith having a first working face in opposition to the working face of the first stationary platen and a second working face in opposition to the working face of the second stationary platen and movable between the first and second stationary platens so as to alternately apply a clamping force to the working face of the first stationary platen and to the working face of the second stationary platen in a clamping position; each stationary platen has mounted thereto a hydraulic actuating cylinder having open ends, wherein the actuator comprises a piston rod disposed through each of the actuating cylinders, each piston rod having a piston head disposed within the respective actuating cylinder and a piston head disposed within the clamping cylinder, an end of each piston extending out of the outer end of the respective actuating cylinder and comprising an enlargement for anchoring the piston rod in the clamping position, whereby actuating the clamping cylinder when the piston rod is anchored applies a clamping force between the moving platen and one of the stationary platens; the piston head disposed within the actuating cylinder comprises a bearing surface formed in the piston rod; the piston rods are engaged to the same piston head within the clamping cylinder; and/or a plurality of actuating cylinders are mounted about the stationary platen for respectively actuating a plurality of pistons disposed within the actuating cylinders and engaged to piston heads disposed within hydraulic clamping cylinders mounted to the moving platen.
The invention further provides a method of clamping opposed first and second structures movable between an open position in which the first and second structures are spaced apart and a closed position in which the first and second structures are disposed together, by a piston extending out of ends of an actuating cylinder mounted to the first structure and having a first portion providing a piston head disposed within the actuating cylinder and a second portion providing a piston head disposed within a clamping cylinder mounted to the second structure, the actuating cylinder having an inner end facing the second structure and an outer end, the method comprising the steps of: a. actuating the actuating cylinder to draw the second structure toward the first structure, b. anchoring the piston, and c. actuating the clamping cylinder to clamp the second structure to the first structure.
In further aspects of the method of the invention: the clamping cylinder has a larger diameter than the actuating cylinder; the piston is anchored by a piston lock comprising an enlargement at a portion of the piston projecting beyond the outer end of the actuating cylinder; the step of anchoring the piston further comprises the step of blocking movement of the enlargement to substantially prevent the piston from extending toward the second structure; the first structure is stationary and the second structure is movable; the first structure comprises a stationary frame comprising at least one stationary platen having a working face, and the second structure comprises a moving frame comprising a moving platen disposed in alignment with the stationary platen and having a working face in opposition to the working face of the stationary platen, the movable platen being movable toward and away from the stationary platen and in a clamping position applying a clamping force between the working face of the stationary platen and the working face of the moving platen; the stationary frame comprises a first stationary platen having a working face and a second stationary platen having a working face disposed in opposition to the first stationary platen, each stationary platen and the moving frame comprises a moving platen disposed between the first and second stationary platens and in alignment therewith having a first working face in opposition to the working face of the first stationary platen and a second working face in opposition to the working face of the second stationary platen and movable between the first and second stationary platens so as to alternately apply a clamping force to the working face of the first stationary platen and to the working face of the second stationary platen in a clamping position; the piston rods are engaged to the same piston head within the clamping cylinder; and/or a plurality of actuating cylinders are mounted about the stationary platen for respectively actuating a plurality of pistons disposed within the actuating cylinders and engaged to piston heads disposed within hydraulic clamping cylinders mounted to the moving platen.